) 1) One who mistakenly ate in the middle of the fast, and then remembered that it was a fast, or, G-d forbid, ate deliberately, should not continue eating. He must continue fasting until the end of the day. (Mishne Berurah 549,3 568,1)
3) 2) Even one who forgot and ate on a communal fast, may say the prayer of “Anenu” during the afternoon services. (Mishne Berurah ibid)